Airfoil shapes used as Horizontal/Vertical Stabilizers  
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All Forums >> RC Airplanes >> Aerodynamics >> Airfoil shapes used as Horizontal/Vertical Stabilizers
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Airfoil shapes used as Horizontal/Vertical Stabilizers - 2/13/2008 3:02:41 AM   
iron eagel



Posts: 1212
Joined: 7/15/2004
From: Middleboro, MA, USA
Status: offline 		I am in the process of designing a airfoil shaped horizontal stabilizer to replace the slab design on an Sig Somethin Extra I am building. Here is the questions I have:
From an aerodynamic standpoint is it ok to go from say 3/8 thick at the root (thickest part of the airfoil) and taper that to 1/8 or so at the tip, to reduce drag. The theory I am working with here is the sheathing at an angle to the tip and root should add a bit of stiffness to the stabilizer and the reduced frontal area should reduce the drag.
The second part of my question is, will this reduce the effectiveness of the elevator where it is essentially a high aspect ratio wing given the overall deign of the stabilizer/elevator combo?
I am also considering treating the vertical stabilizer and rudder in the same manner, am I going to cause myself any problems by doing this?


_____________________________

The Wrights never crashed, they only had hard landings. I 've had some hard landings myself. AMA EAA AOPA revver #185
       Post #: 1

RE: Airfoil shapes used as Horizontal/Vertical Stabili... - 2/13/2008 3:38:42 AM   
pimmnz


 

Posts: 499
Joined: 11/9/2005
From: Auckland, NEW ZEALAND
Status: offline 		There will be no aerodynamic differences that you will notice while flying by using a symmetric (zero camber) section on the tail surfaces. The tailplane/elevator is actually just a variable camber airfoil anyway, not two 'wings' hinged together. The fin/rudder is essentially the same. No doubt there will be plenty of other opinions, but the proof of the pudding etc. is when you fly the thing anyway.
Evan, WB #12.

(in reply to iron eagel)
       Post #: 2

RE: Airfoil shapes used as Horizontal/Vertical Stabili... - 2/13/2008 3:40:27 AM   
BMatthews



Posts: 8893
Joined: 10/4/2002
From: Burnaby, BC, CANADA
Status: offline 		Look again at the wing on the Sumthin' Extra. Now tell me again why you're worried about reducing drag in an airfoiled stabilizer?

As for thick vs thin..... Normally a thicker section tends to stall at a higher angle of attack than a thin one. But with stabilizers and fins it's a different story since they are variable camber sections due to the fixed and moving portions. So the rules the wing follows don't totally apply. The variable camber means that a thicker section isn't as important. This is why a lot of classic planes can happlily get away with flat tail airfoils.

All that being said it's possible that the airfoil nose will help keep the air more attached up to a point but given the deflection angles used in a not of 3D airplanes avoiding a stall is near impossible. But just because the tail sections are stalled in the rear half doesn't mean the tails stop lifting. They still do that very well.


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Bruce-
Proudly wasting balsa since 1965.

Free Flighters go that extra mile........

(in reply to iron eagel)
       Post #: 3

RE: Airfoil shapes used as Horizontal/Vertical Stabili... - 2/13/2008 3:58:26 AM   
iron eagel



Posts: 1212
Joined: 7/15/2004
From: Middleboro, MA, USA
Status: offline 		Bruce and Evan,
Thanks a lot for taking the time to reply!
I know given the main wing I am not going to gain all that much in performance given the time and effort to build airfoil shape tail section. I was just concerned that by using the taper from the root to the tail I would increase the span-wise flow and mess up the effectiveness of the rudder and elevator.
And where my knowledge is limited I had no idea that it is considered as a variable camber airfoil to start with.

As far as going through all the pain and anguish to build such component into this plane is mostly for practice to refine my building techniques when I get into airplanes where it will really matter, such as large scale or high speeds.

Sorry for pestering you with questions but as I sit sanding balsa for skins and work out the design of the tail feathers I would like to use, these questions keep popping into my mind, and I feel the need to get some input from those with more knowledge than myself. I have formal training in engineering (electrical, not mechanical or aerodynamics) and not knowing all the ins and outs to aerodynamics and structural engineering I keep coming up with these questions during the course of my build.

< Message edited by iron eagel -- 2/13/2008 4:02:17 AM >

_____________________________

The Wrights never crashed, they only had hard landings. I 've had some hard landings myself. AMA EAA AOPA revver #185

(in reply to BMatthews)
       Post #: 4

RE: Airfoil shapes used as Horizontal/Vertical Stabili... - 2/13/2008 7:26:11 AM   
pimmnz


 

Posts: 499
Joined: 11/9/2005
From: Auckland, NEW ZEALAND
Status: offline 		Iron Eagle,
There are no stupid questions, but you find that you will get some really 'interesting' answers...!
Evan.

(in reply to iron eagel)
       Post #: 5

RE: Airfoil shapes used as Horizontal/Vertical Stabili... - 2/13/2008 12:34:38 PM   
da Rock



Posts: 6370
Joined: 10/11/2005
From: western, NC, USA
Status: offline 		iron eagle,
While you're mulling over the astute answers, remember that the beauty of our hobby is that we always get 100% truthful answers from the model. And take comfort that seldom does anything we try cause major changes.

The really good benefit from built up stabs is strength. And often there is no significant increase in weight. win win The really fun return on the time and effort is that YOU will see just how little increase in weight you got and will be able to tell newbies your findings..... and then join the masses that THEY REFUSE TO BELIEVE.

As for the thickness taper causing problems. No real problems with a tail.

Thickness tapers by themselves actually don't do much. But if they are not in proportion to the change in chord from root to tip, they cause a change in the airfoil from root to tip. That might matter in a wing. And it might be a good thing.

Control Line precision aerobatics guys very often built wings with tapering planform. And usually changed the thickness from root to tip. And did it sometimes to reduce the tip stall potential. They tapered the thickness LESS than they tapered the chord and wound up with a wing that still tapered down in both thickness and chord. But by having a slightly "thicker" airfoil at the tip, got a later stalling tip.

Fun thing about all that high tech description and discussion? Nobody can really prove you wrong. And most judges couldn't even follow the ideas, so were suitably impressed. Which was the point of talking about it in the first place. Good thing was that it actually did seem to work. And if it seems to work for you, it is working for you.

(in reply to pimmnz)
       Post #: 6

RE: Airfoil shapes used as Horizontal/Vertical Stabili... - 2/14/2008 2:11:47 AM   
iron eagel



Posts: 1212
Joined: 7/15/2004
From: Middleboro, MA, USA
Status: offline 		Da Rock,
Thanks again for your thoughts...
You know that keeping the weight down is one of my primary considerations as I progress with this build. The next and primary reason for these modifications is strength of the structure so I can eliminate the external brace wires and the weight of their entire assembly. I weighed the balsa components used in the construction of the stock tail feathers (Horiz. and Vert. Stabs., Rudder and elevator and found that they weigh a total of 2 Oz alone. I will also weigh the guy wires, and mounting hardware and add that to the total and see if my built up system will less than that total if possible, and I would feel like I made some progress.

I know at the Rn's we work at drag reduction is looked at as a "black art" of some sort and any real gains are probably to small to really notice or even measure without a lot of fancy instrumentation....


I like a nice "clean" airframe on an aircraft from the looks, as much as any performance enhancement gained.
Not to mention ,it is neat that we can experiment with these types of things, just because we can.


_____________________________

The Wrights never crashed, they only had hard landings. I 've had some hard landings myself. AMA EAA AOPA revver #185

(in reply to da Rock)
       Post #: 7

RE: Airfoil shapes used as Horizontal/Vertical Stabili... - 2/14/2008 2:28:32 AM   
HighPlains


 

Posts: 2640
Joined: 3/2/2003
From: Over da rainbow, KS, USA
Status: offline 		Sounds like you are looking to put a expensive English riding saddle on a pig and expecting to ride a throughbred. Not going to happen. The result of any drag reduction would be buried in the wake of the rest of the airframe. On a design like that, weight reduction would be noticed, little else.

_____________________________

In politics if you want anything said, ask a man. If you want anything done, ask a woman - Margaret Thatcher

(in reply to iron eagel)
       Post #: 8

RE: Airfoil shapes used as Horizontal/Vertical Stabili... - 2/14/2008 4:45:50 AM   
iron eagel



Posts: 1212
Joined: 7/15/2004
From: Middleboro, MA, USA
Status: offline 		HighPlains you are indeed correct...

I am just trying to spruce the pig up a bit, while trying to hone my design and building skills a bit, and hopefully gain some more knowledge in the process....
Hopefully the weigh reductions thus, far along with the reduced weight in the tail ,will offset the weight of the wing fairings I am adding to blend the wing into the fuselage. The intent with the fairings is to help reduce the turbulent airflow along the rest of the airframe.
In the end how will it perform, probably a lot like an SE.


_____________________________

The Wrights never crashed, they only had hard landings. I 've had some hard landings myself. AMA EAA AOPA revver #185

(in reply to HighPlains)
       Post #: 9

RE: Airfoil shapes used as Horizontal/Vertical Stabili... - 2/14/2008 2:33:21 PM   
dick Hanson



Posts: 9930
Joined: 12/12/2001
From: slc, UT, USA
Status: offline 		forget the streamlining
look at the wing/stab/elevator rudder fin-- from a structural point of view
If yo u make the lightest structure which will still be strong enough- you have done your job correctly.
flat , rounded a little , who cares .
It is actually getting structure correct at the lowest weight ,that really counts.

Don't believe this ?
OK
turn back the pages of time -to the first half of the 20th century - look at the evolution of tail groups
Typically the air pressure on the elevator tends to deflect the stabilizer - so take care of twisting loads
bending loads should be obvious if you have some basic engineering.
stabs need to be STIFF-- elevators - not as stiff .

< Message edited by dick Hanson -- 2/14/2008 2:34:01 PM >

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Libby

(in reply to iron eagel)
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RE: Airfoil shapes used as Horizontal/Vertical Stabili... - 2/14/2008 2:54:54 PM   
da Rock



Posts: 6370
Joined: 10/11/2005
From: western, NC, USA
Status: offline 		The beauty of our hobby is that we can do whatever we want. For whatever reason we wish.

And then when our latest enhancement flies, it proves us right.

Hey, it IS faster, isn't it. Watch that sucker go. It's gotta be 5 maybe 10mph faster than it would be otherwise, RIGHT!

So if you like the streamlining, do it. It WILL make a better model for you. And you can prove it. Or not. But they can't prove otherwise. And you both won. You both got what you wanted. A model that suits you.

Does everything we do make a difference? Yeah, to us.

(in reply to dick Hanson)
       Post #: 11

RE: Airfoil shapes used as Horizontal/Vertical Stabili... - 2/14/2008 4:18:50 PM   
The Internet Killer


 

Posts: 222
Joined: 8/21/2005
From: Ferndale, WA, USA
Status: offline
quote:

ORIGINAL: HighPlains

Sounds like you are looking to put a expensive English riding saddle on a pig and expecting to ride a throughbred.


Now there was a picture I could have done without seeing.

Last time I bought an english saddle the pig rode on it!! LOL



Sorry, I must have issuses.

_____________________________

Hindsight is an exact science.

(in reply to HighPlains)
       Post #: 12

RE: Airfoil shapes used as Horizontal/Vertical Stabili... - 2/15/2008 1:07:35 AM   
iron eagel



Posts: 1212
Joined: 7/15/2004
From: Middleboro, MA, USA
Status: offline
quote:

ORIGINAL: The Internet Killer


quote:

ORIGINAL: HighPlains

Sounds like you are looking to put a expensive English riding saddle on a pig and expecting to ride a throughbred.


Now there was a picture I could have done without seeing.

Last time I bought an english saddle the pig rode on it!! LOL



Sorry, I must have issuses.
It seems the only issue you may have is with the pigs...
LOL

Anyhow thanks for the input guys now time to get back to the build. I listed it as: Yet another Something Extra build in the kit forum, but it should have been titled more along the lines of a bash rather than a build, perhaps...

Anyhow, as far as the modification since it was my intent to max out a Sig SE since I am building a new stab and vertical fin assembly anyhow I wondered if I could enhance it, without causing other issues with the flight handling of the plane and perhaps gain some small amount of performance out of the basic design.

Thanks again everyone!
Regards,
Paul

< Message edited by iron eagel -- 2/15/2008 1:09:10 AM >

_____________________________

The Wrights never crashed, they only had hard landings. I 've had some hard landings myself. AMA EAA AOPA revver #185

(in reply to The Internet Killer)
       Post #: 13

RE: Airfoil shapes used as Horizontal/Vertical Stabili... - 2/15/2008 1:18:33 AM